1. Field of the Invention
Apparatuses consistent with the present invention relate to a magnetic head, and more specifically, to a magnetic head having a magnetic thin film structure that can effectively reduce an external stray field by improving the structure of the magnetic thin film of a head yoke that includes a first pole P1 and a second pole P2, and enables a high speed magnetization reversal of a head yoke for high density information recording.
2. Description of the Related Art
Much research is performed into increasing the recording density of magnetic information recording devices. High density recording requires a magnetic head design that can record data at a high speed.
FIG. 1 is a cross-sectional view illustrating a recording unit of a conventional magnetic head. As depicted in FIG. 1, a recording unit of a magnetic head 10 records a magnetic signal to a recording medium 9 using a first pole P1 and a second pole P2 to form a leakage flux that magnetizes the recording medium 9, and induction coils 5 that induce a magnetic field in the first pole P1 and the second pole P2.
Here, the characteristics of the first and second poles P1 and P2, especially their magnetic characteristics, control the quality of the magnetic field input to the recording medium 9. A recent trend is that as recording a real density increases, the bit size of the recording medium is reduced. Accordingly, the material for forming the first and second poles P1 and P2 requires a soft magnetic property having highly saturated magnetization, high permeability, low coercivity and rapid response to the applied field.
However, the poles P1 and P2 of the magnetic head 10 are also very sensitive to external magnetic fields. For example, a magnetic field (hereinafter, a stray field) generated by external magnetic generation sources other than the induction coil 5, such as a VCM that moves the magnetic head 10 over the recording medium, can enter the first and second poles P1 and P2. Therefore, efforts have been made to reduce the effect of stray fields, mainly in connection with the structure of a shield layer that shields stray fields, since any stray fields can cause recording or erasing errors.
The main difference between the writing field and the stray field is their frequency. The writing field has a very high frequency˜MHz, while the stray field is almost static, that is constant with time.
On the other hand, the first and second poles P1 and P2 of the magnetic head 10 that record at high speed must be formed of a soft magnetic material in which flux is forward/reverse transformed at a high speed corresponding to a current with a high frequency. FIG. 2 is a graph showing how the magnetization M of a magnetic thin film lags behind a magnetic field H applied by an induction coil 5. In the graph, the x axis represents time and the y axis represents the magnitude of the applied magnetic field H indicated as a dotted line and the normalized magnetization M of the magnetic thin film indicated as curved lines from a1 through a6. The bold solid line a1 is a magnetization curve of the magnetic thin film corresponding to conventional first and second poles P1 and P2 according to time. Referring to the dotted line in the graph, the magnetic field H is initially applied at a magnitude of +400 kA/m and is gradually changed to a magnitude of −400 kA/m after 0.25 nanoseconds. This state is maintained for 1 nanosecond, after which the magnitude is gradually changed to +400 kA/m after 0.25 nanoseconds. The curve a1 corresponding to the dotted line lags behind the dotted line from the x axis view. When the dotted line and the curved line a1 are compared, it is seen that the magnetization M of the magnetic thin film is delayed with respect to the applied magnetic field H.
The magnetic head 10 moves relative to the recording medium 9, since the recording medium 9 rotates at a constant speed below the magnetic head 10. Therefore, a magnetic field must be formed within a specified time by supplying a current to the induction coil 5 so that the magnetic head 10 can record information on a desired location on the media. However, as depicted in FIG. 2, recording information at a high speed is difficult because the magnetization M of the first and second poles P1 and P2 lags behind the magnetic field H applied by the induction coil 5. Therefore, to record at a high speed, there is a need to redesign the magnetic head so that the magnetization reversal of the first and second poles P1 and P2 can be performed at a high speed corresponding to the high frequency current.